Kappus
From Halopedia, the Halo wiki
Private Kappus was a specialist in the squad, that also housed Private Manuel Mendoza, Private Bicenti, Private Riley, Private Jenkins, and Sergeant Johnson.
He was a specialist in Covenant and Forerunner technology. One of his tasks was opening locked doors. He was ordered by Captain Keyes to open the door that just so happend to be the only thing holding back the flood. Unwillingly and unknowingly, Kappus unleashed the Flood on Installation 04, dooming him and the rest of his squad, save for Johnson. When an Infection Form attached itself to Kappus friend Riley, he got it off successfully. Kappus was soon transformed into a Combat Form, though.
Trivia
His role in the game is often mistaken for that of Mendoza's.
